This invention relates to non-contact sensing of motion of a vibrating element on vibratory compacting machines. More specifically, the invention relates to use of a non-contact sensor and control system to determine and control vibrational amplitude, vibrational frequency, phase, and vibrational waveform of vibrating elements.
Vibratory compacting machines are used to compact soils, compact refuse, compact asphalt pavement, and for other purposes. Vibratory compacting machines often include one or two heavy steel drums which are capable of compacting surfaces by rolling over them. Alternatively, machines may incorporate a vibrating plate which serves a similar purpose. Each vibrating element may include a means of vibrating a element for enhanced compacting performance. For example, the roller drum may contain an eccentric mass turned by hydraulics. This allows the drum to shake. The eccentric mass may be turned at different speeds thus causing differing intensities and frequencies of vibration. Asphalt pavement, soils, and other materials are alternatively compacted by a weighted vibrating plate which is slid across the surface.
The intensity of vibration is related to the speed at which the eccentric mass is turned, and the geometry and mass of the eccentric mass. Where an eccentric mass is revolved to create a vibration, turning the eccentric mass at increased speeds results in increased intensity of the vibration of the roller drum. A heavier eccentric mass, or a more eccentric mass will also cause more intense vibration. Where an eccentric mass is the mechanism for vibrating a roller drum, the drum will move (vibrate) up and down once with each rotation of the of the eccentric mass. In other words, if the eccentric mass is rotating at 3000 revolutions per minute (3000 RPM), then the drum will be vibrating at 3000 vibrations per minute (3000 VPM). Most vibratory compacting machines have a mechanism for adjusting the speed of rotation of the eccentric mass. Some vibratory compacting machines also have a mechanism for adjusting or selecting one of several eccentric masses to be rotated. Selection of optimal rotational speed (vibrational frequency) and optimal eccentric mass setting will result in the desired compacting performance. Selection of non-optimal rotational speed and eccentric mass setting could lead to poor or undesired compacting performance, operator discomfort, or excessive wear and damage to the vibratory compacting machine. The present invention is capable of measuring and controlling vibrational speed, vibrational amplitude, and vibrational phase regardless of the mechanism used to cause such vibration.
Currently, speed sensors are used to measure the rotational speed of an eccentric mass. Speed sensors are often incorporated into hydraulic motors which are often used to turn eccentric masses within vibrating elements. One common type of speed sensor creates a fixed number of electrical pulses for each rotation of the shaft. A speed sensor may also incorporate a means of determining its absolute position within the rotational cycle. One embodiment of an absolute position sensor is a system that produces an electrical pulse at a certain fixed point during each revolution of a rotating shaft. Examples of using speed sensors are given in U.S. Pat. No. 5,325,055 to Gerringer.
Although the speed of rotation and therefore frequency of vibration are determined from use of a speed sensor, information concerning the vibration of the roller drum is not determined. In particular, the vibration amplitude is not determined, and the phase of the vibration, and vibration waveform are not determined.
Other attempts have also been made at improving the quality of information that can be derived from a sensor. For example, piezoelectric accelerometers have been used for the purpose of measuring roller drum vibration. If a piezoelectric accelerometer is mounted to the roller drum, a means must be provided to send the vibration measurements from the rotating drum to the fixed portion of the machine. Wires are not used since wires would become wrapped up and twisted by the rotation of the roller drum. Radio telemetry or slip ring systems may be used for this purpose during development and testing of a vibratory compactor. Factors such as cost and reliability prevent such systems from being widely used in production machines.
Another prior art attempt has used magnetic circuits. For example, U.S. Pat. No. 4,330,738 to Paramythioti et al uses a magnetic circuit as a vibration pickup. One deficiency of this type of system is that the vibration pickup requires a marker armature of magnetic material in contact with the vibrating element in order to complete the magnetic circuit and therefore is not a non-contact sensor. Further, this arrangement is susceptible to magnetic interference resulting in imprecision and/or errors in measurement.
Therefore, there are a number of problems associated with determining and controlling vibration of roller drums. Thus, it is a primary object of the present invention to provide an improved system and method for determining vibratory motion of a vibrating element.
Another object of the present invention is to provide a system and method for determining vibratory motion of a roller drum that does not require contact between a sensor and the vibrating element.
A further object of the present invention is to provide a system and method for non-contact sensing of motion of a vibrating element that can determine the amplitude of vibration of the vibrating element.
Yet another object of the present invention is to provide a system and method for non-contact sensing of motion of a roller drum that provides for determining the frequency of vibration of a vibrating element.
A still further object of the present invention is to provide a system and method for non-contact sensing of motion of a vibrating element that provides for determining a phase difference between a first vibrating element and a second vibrating element.
Another object of the present invention is a system and method for sensing and controlling the phase difference between the rotation of an eccentric and the vibrational motion of a vibrating element.
Yet a further object of the present invention is to provide a system and method for sensing of motion of a roller drum that provides for independently adjusting a vibratory motion in one or more vibratory elements based upon the sensed vibratory motion.
Another object of the present invention is to provide a method and system for determining the selection or adjustment of the eccentric mass that should be used to cause desired vibratory motion.
Another object of the present invention is to provide a system and method for non-contact sensing of motion of a roller drum that is low cost and mass producable.
Another object of the present invention is the ability to prevent undesired vibrations of the framework to which the sensor might be attached from interfering with the ability of the sensor to make accurate measurements.
Another object of the present invention is a system which is capable of determining the precise waveform of vibratory motion of a vibrating compaction element.
It is a further object of the present invention to provide a method and system for non-contact sensing of motion of a roller drum that does not rotate with the drum.
These and other objects of the present invention will become apparent from the following description.
The invention is a system and method for non-contact sensing and control of the motion of vibrating compaction elements. A non-contact sensor uses radio, radar, microwave, light, optical, sonic, acoustic, capacitive proximity, or inductive proximity sensing to determine the vibratory motion of a roller drum. Such a device is capable of sensing the vibrational amplitude, vibrational frequency, vibrational phase difference between two or more elements. A control system which is able to sense these vibrational characteristics is able to optimize speed, phase, and eccentric mass of each of the one or more eccentrics which vibrate one or more vibrating compacting members. A further feature of the present invention is a means of insuring that accurate measurements are made even if the machine member to which the sensor is mounted experiences undesired vibrations. As this additional information concerning motion of the vibrating element is detected in the current system, improved control results.
In particular, the present invention provides for control that is based upon the actual vibratory motion of one or more vibrating elements, as opposed to merely being based upon motion of an eccentric mass or other means of vibration within the vibrating element. As the vibratory motion of the vibrating element is measurable with the present invention, the information needed for improved control is available.